I've got difficulties to solve this electronic exercise

[Bricolo]

Originally posted by phase_accurate


Simply add an emitter resistor to T1. And use a proper voltage divider for its base.

Regards

Charles

the need for a voltage divides on the base is obvious, but why the emirrer resistor?

I see one advantage in this: increasing the input impedance. Are there any other ones?

[phase_accurate]

Are there any other ones?

Temperature stability

Regards

Charles

[sreten]

Originally posted by phase_accurate


Simply add an emitter resistor to T1. And use a proper voltage divider for its base.

Regards

Charles

And an emitter follower to the output, as gain is too
dependent on RL. For Audio cascoding T1 is fairly pointless.

But two transistor circuits work much better with feedback :

http://www.dself.dsl.pipex.com/ampins/discrete/twoq.htm


sreten.

[Bricolo]

Another problem

I have to calculate R and Rs.
Both transistors have the same bias points


Method1:
Vgs=-0.9V
Since Vg=0V, S is at 0.9V (23.1 for the upper transistor)
Id=4mA so R=Rs=U/I=0.9/0.004=225R

Right?



Method2:
Vds=8.5V
Id=4mA

So
E=R*Id+Vds+Vds+Rs*Id
-> 7V left for the resistors. 3.5V on each since the bias is identical for both transistors.
That gives Rs=R=3.5/0.004=875R



The results aren't the same for both methods